Method for forming copper interconnection structures

ABSTRACT

A method for forming a copper interconnection structure includes the steps of forming an opening in an insulating layer, forming a copper alloy layer including a metal element on an inner surface of the opening, and conducting a heat treatment on the copper alloy layer so as to form a barrier layer. An enthalpy of oxide formation for the metal element is lower than the enthalpy of oxide formation for copper. The heat treatment is conducted at temperatures ranging from 327° C. to 427° C. and for a time period ranging from 1 minute to 80 minutes.

This application claims priority under 35 U.S.C. §119 from Japanesepatent application serial No. 2008-324061, filed Dec. 19, 2008, entitled“Method for forming copper interconnection structure, copperinterconnection structure and semiconductor device”, which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a method for forming a copperinterconnection provided with an interconnection body made of copper onan electric insulating layer, the copper interconnection structure, anda semiconductor device provided with the copper interconnection on theinsulating layer as a circuit interconnection.

BACKGROUND OF THE INVENTION

In order to fabricate semiconductor devices with higher speed and lowerpower consumption, silicon based integrated circuits (ICs) or thin filmtransistors (TFTs), or the like (refer to patent document 1) arerequired featuring a low RC delay interconnection pattern (refer tonon-patent document 1 below). Examples of such a semiconductor devicesmay include high-speed central processing units (CPUs) or large-sizeliquid crystal display (LCD) devices. Further, in silicon based ultralarge integration (ULSI) systems, interconnections with low electricalresistivity are required to increase their integration density eventhough they may include interconnection with small width. In addition,in order to fabricate semiconductor devices with higher reliability,interconnections made from materials which are superior inelectro-migration (EM) and stress-migration (SM) resistance are required(refer to patent document 1 below).

[Patent document 1] Japanese unexamined patent application No.H11-186273

[Non-Patent Document 1] “Semiconductor Device (2^(nd) edition)—Physicsand Technology” by S. M. Sze (Oct. 5, 2005, Sangyo Tosho, Co., Ltd.,third impression of second edition, P 345-346.

To achieve the aforementioned needs, a technique is disclosed to forminterconnections for the semiconductor devices described above usingcopper (Cu) as an interconnection body. Copper has a lower resistivitycompared to aluminum (Al) or an aluminum alloy, such as aluminum coppersilicon (AlCuSi) alloy, and is superior in electro-migration EMresistance (refer to patent document 1 above and patent documents 2-6below). For example, a technique is disclosed to form a damascene typeinterconnection structure having an interconnection body made of copperformed on an insulating layer containing silicon, such as SiO₂, througha diffusion barrier layer, thereby preventing copper from diffusing intothe insulating layer (refer to patent documents 7 and 8 below).

-   [Patent document 2] Japanese unexamined patent application    publication no. S63-156341-   [Patent document 3] Japanese unexamined patent application    publication no. H01-202841-   [Patent document 4] Japanese unexamined patent application    publication no. H05-047760-   [Patent document 5] Japanese unexamined patent application    publication no. H06-140398-   [Patent document 6] Japanese unexamined patent application    publication no. H06-310509-   [Patent document 7] Japanese unexamined patent application    publication no. H11-054458-   [Patent document 8] Japanese unexamined patent application    publication no. H11-087349

In the above mentioned copper interconnection, the diffusion barrierlayer has conventionally been made from manganese (Mn) (refer to patentdocument 5 above and patent documents 9 and 10 below), or boride ornitride of manganese (Mn) (refer to patent document 5 above), tantalum(Ta) (refer to patent document 2 above), chromium (Cr) (refer to patentdocuments 2 and 3 above), titanium (Ti) (refer to patent document 3above), titanium nitride (TiN) (refer to patent documents 1 and 2above), tungsten (W) (refer to patent document 2 above), molybdenum (Mo)(refer to patent document 2 above), zirconium (Zr) (refer to patentdocument 3), vanadium (V) (refer to patent document 3 above), niobium(Nb) (refer to patent document 3 above), nitride film of Zr, Ti, V, Ta,Nb, Cr, or boron compound film (refer to patent document 3 above), andthe like.

Also, a technique for forming a diffusion barrier layer from amultilayer structure has been disclosed (refer to patent document 6above). The technique disclosed in the patent document 6 prevents copperfrom diffusing into the SiO₂ insulating layer by providing a “traplayer” made of manganese (Mn) or magnesium (Mg) around the diffusionbarrier layer, or as a base of the diffusion barrier layer which is madefrom tantalum (Ta), tungsten (W), or tantalum.tungsten (Ta—W) alloy.

Copper constituting the interconnection body is formed on the barrierlayer by an electrolytic plating method, sputtering method (refer topatent documents 9 and 10 below), or plasma CVD (chemical vapordeposition) method (refer to patent document 11 below). As an example, acopper layer for an interconnection made of (111), (200), and (311)crystal faces is formed on a niobium (Nb) layer (refer to patentdocument 11 above). In order to uniformly form a copper interconnectionbody over a barrier layer, another technique is also disclosed where thecopper interconnection body is formed through a seed layer, which isformed from a thin layer of copper (refer to patent document 12 below).For example, the copper layer of an interconnection formed by theelectrolytic plating method over a thin layer of copper, which in turnis formed on a tantalum nitride (TaN) layer by a sputtering method, doesnot constitute a surface with uniform crystal face indexes. Instead, thesurface is constituted from crystal faces with different indexes, suchas (111), (200), and (311) crystal faces (refer to patent document 10).

[Patent document 9] Japanese unexamined patent application publicationno. 2005-277390

[Patent document 10] Japanese unexamined patent application publicationno. 2003-142487

[Patent document 11] Japanese unexamined patent application publicationno. H05-190548

[Patent document 12] Japanese unexamined patent application publicationno. 2006-049641

In recent years, another technique has been disclosed in that, ratherthan forming separately a barrier layer from tantalum or tantalumnitride and a copper seed layer over the barrier layer for forming thecopper interconnection body, forming both of the above layers in a selfforming manner (refer to patent document 9 above and patent document 13below). For example, a technique has been known to form a diffusionbarrier layer, in which its surface layer is a layer mainly composed ofcopper. The diffusion barrier layer is formed from a copper alloy layerwith an alloying metal element and is formed on an insulating layercontaining silicon (refer to patent documents 9 above, and patentdocument 13 below).

[Patent document 13] Japanese patent no. 4065959

According to the above mentioned technique, the copper interconnectionbody may easily be structured using the layer mainly composed of copperformed on the surface portion of the diffusion barrier layer. In thistechnique, the layer mainly composed of copper is used as a copper seedlayer for forming the diffusion barrier layer in a self forming manner.Examples of the metal alloying element in the copper alloy layer mayinclude manganese (Mn), niobium (Nb), zirconium (Zr), chromium (Cr),vanadium (V), yttrium (Y), rhenium (Re) and the like (refer to patentdocument 9 above).

The metal element described above has a diffusion coefficient greaterthan the self diffusion coefficient of copper and the metal element isoxidized more easily compared to copper (refer to patent document 13).In order to form a diffusion barrier layer in a self forming manner froma copper alloy layer or a solid solution layer containing the abovementioned metal elements as a material, it is common to conduct heattreatment on the copper alloy layer or the solid solution layer, afterdepositing these layers on an insulating layer (refer to patentdocuments 9 and 13 above).

An advantage of using the copper alloy or solid solution layerscontaining a metal element having a diffusion coefficient greater thanthe self diffusion coefficient of copper and being oxidized more easilycompared to copper, is that the diffusion barrier layer, in which itssurface layer is mainly composed of copper (copper seed layer), may beformed in a self forming manner by conducting the heat treatment.Meanwhile, however, there has been a problem in that the surface layerof the diffusion barrier layer, which is mainly composed of copper, ismade from various crystallographic faces (crystal face) when thediffusion barrier layer is formed by heating the copper alloy layer orthe solid solution layer containing such additive elements.

A concrete example of such a technical disadvantage resulted from theabove mentioned problem is the possibility of providing a copperinterconnection with a large amount of crystal grain boundaries on thesurface layer of the diffusion barrier layer which is mainly composed ofcopper. When a large amount of crystal grain boundaries are present inthe copper interconnection, the diffusion of copper constituting theinterconnection body through the grain boundaries occurs significantly,thereby electro-migration (EM) resistance and stress-migration (SM)resistance are decreased. Further, the insulating property of theinsulating layer is decreased for a damascene type copperinterconnection structure. Therefore, the achievement of semiconductordevices with high operating reliability has not yet been met.

The present invention is made under the above-mentioned situation. Thepurpose of the present invention is to reduce the density of crystalgrain boundaries, present in the copper interconnection body, by forminga barrier layer in which the kinds of copper surface orientation aredecreased. Therefore, the purpose of the present invention is to providecopper interconnection structures with low electrical resistance andwith improved electro-migration (EM) and stress-migration (SM)resistance.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method forforming a copper interconnection structure includes the steps of:

forming an opening in an insulating layer;

forming a copper alloy layer including a metal element on an innersurface of the opening, wherein an enthalpy of oxide formation for themetal element is lower than the enthalpy of oxide formation for copper;and

conducting a heat treatment on the copper alloy layer so as to form abarrier layer, wherein said heat treatment is conducted:

at temperatures ranging from 327° C. to 427° C., and

for a time period ranging from 1 minute to 80 minutes.

As described above, in the first aspect of the present invention theheat treatment is applied under the predetermined condition for formingthe barrier layer. Accordingly, the formation of the barrier layer withreduced number of copper surface orientations is possible at the surfaceof the barrier layer. Therefore, the density of crystal grainboundaries, present in the copper interconnection body, is decreasedsuch that copper interconnection structures with low electricalresistance and with improved electro-migration (EM) and stress-migration(SM) resistance are realized.

In accordance with a second aspect of the present invention, a methodfor forming a copper interconnection structure includes the steps of

forming an opening in an insulating layer;

forming a copper alloy layer including a metal element on an innersurface of the opening, wherein the enthalpy of oxide formation for themetal element is lower than the enthalpy of oxide formation for copper,and

applying a heat treatment to the copper alloy layer so as to form abarrier layer such that the kinds of copper surface orientation isreduced at an inner surface of the barrier layer.

According to the second aspect of the present invention, as describedabove, the heat treatment is applied to the copper alloy layer. Due tothis heat treatment, a barrier layer with a reduced number of coppersurface orientations is formed at the inner surface of the barrierlayer. Accordingly, the density of crystal grain boundaries, present inthe copper interconnection body, is decreased. Therefore, therealization of copper interconnection structures with low electricalresistance and with improved electro-migration (EM) and stress-migration(SM) resistance is possible.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an X-ray diffraction pattern taken from the surfaceof a copper layer deposited on a magnesium layer, before applying a heattreatment.

FIG. 2 illustrates an X-ray diffraction pattern taken from the surfaceof a copper layer deposited on a magnesium layer, after applying a heattreatment.

FIG. 3 illustrates an X-ray diffraction pattern taken from the surfaceof a copper layer deposited on a germanium layer before applying a heattreatment.

FIG. 4 illustrates an X-ray diffraction pattern taken from the surfaceof a copper layer deposited on a germanium layer after applying a heattreatment.

FIG. 5 illustrates schematically the first step of a process formanufacturing an embodiment of a copper interconnection structure.

FIG. 6 illustrates schematically the second step of a process formanufacturing of an embodiment of a copper interconnection structure.

FIG. 7 illustrates an X-ray diffraction pattern taken from the surfaceof a multilayer copper-alloy structure before applying a heat treatment.

FIG. 8 illustrates an X-ray diffraction pattern taken from the surfaceof a multilayer copper-alloy structure, diffusion barrier layer, afterapplying a heat treatment.

FIG. 9 illustrates schematically the third step of a process formanufacturing of an embodiment of a copper interconnection structure.

FIG. 10 illustrates a cross-sectional view of an embodiment of a copperinterconnection structure, manufactured by the process steps shown inFIGS. 5, 6, and 9.

FIG. 11 is an X-ray diffraction pattern taken from the surface of acopper layer deposited on a tantalum layer before applying a heattreatment.

FIG. 12 is an X-ray diffraction pattern taken from the surface of acopper layer deposited on a tantalum layer after applying a heattreatment.

FIG. 13 illustrates a cross-sectional view of an alternative embodimentof a copper interconnection structure.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described hereinafter withreference to the accompanying drawings, in which the preferred exemplaryembodiments of the invention are shown. The ensuing description is notintended to limit the scope, applicability or configuration of thedisclosure. Rather, the ensuing description of the preferred exemplaryembodiments will provide those skilled in the art with an enablingdescription for implementing the preferred exemplary embodiments of thedisclosure. It should be noted that this invention may be embodied indifferent forms without departing from the spirit and scope of theinvention as set forth in the appended claims.

Embodiments of the present invention relates in general to copperinterconnections and their manufacturing process. More specifically, itrelates to a new generation of copper interconnections with improvedelectro-migration (EM) and stress-migration resistance.

Embodiments of the present invention are directed to methods for formingcopper interconnection structures and semiconductor devices capable ofenhancing the EM or SM resistance and improving their operatingreliability. This is achieved by reducing the kinds of copper surfaceorientation on a diffusion barrier layer when the diffusion barrierlayer is formed. The diffusion barrier layer pertaining to the presentinvention is formed by applying a heat treatment to a copper alloy layerwhich contains a metal element. The metal element is easily oxidizedcompared to copper and features a diffusion coefficient greater than theself diffusion coefficient of copper. By reducing the kinds of coppersurface orientations of the barrier layer, the density of crystal grainboundaries present in the copper interconnection body, as well as theelectrical resistance of the copper interconnection, will be reduced.

In order to achieve a copper interconnection body with a low density ofcrystal grain boundaries, the challenge lies in providing a technique inwhich the surface portion of the barrier layer, which is mainly composedof copper, is formed from a limited number of copper surfaceorientations. In order to resolve this technical issue, the inventors ofthe present invention devoted themselves to study every possible factorthat may affect the kinds of copper surface orientation of the barrierlayer.

As a result, the inventors of the present invention have reached thefollowing conclusion: The number of copper surface orientations, in alayer mainly composed of copper, depends on the type of metal elementadded into the copper alloy layer as an additive element. Although, mostof metal elements are easily oxidized compared to copper, only a limitednumber of metal elements are capable of providing a reduced number ofcopper surface orientation in the copper seed layer.

The limited number of metal elements, referred hereinafter as the “metalelement”, exerts the action of reducing the kinds of copper surfaceorientation of the copper alloy layer when the copper alloy layer isexposed to a heat treatment, thereby providing a lower number of coppersurface orientations, over the barrier layer, after applying the heattreatment. The number of copper surface orientations is lower comparedto the time when the copper alloy layer is formed (at deposition) beforeapplying the heat treatment. For example, in the case where a copperalloy layer with three kinds of copper crystal faces is formed atdeposition, the appropriate metal element, added as an alloying elementof the copper alloy layer, may reduce the kinds of copper crystal facesto two after applying the heat treatment.

A diffusion barrier layer, in which its surface layer is a layer mainlycomposed of copper, pertaining to the present invention, is provided onan insulating layer containing low permittivity silicon oxide whichforms an interlayer insulating layer of a damascene type interconnectionstructure. Examples of the insulating layer with low permittivitysilicon oxide may include silicon oxide carbide (SiOC: k˜2.8), siliconfluoride oxide (SiOF: k˜3.6), silicon fluoride carbide (SiCF:k=2.0˜2.4), and silicon dioxide (SiO2: k˜3.9). Organic insulating layerssuch as poly-arelene ether (k˜2.6) and polyimide (k=2.7˜2.9) can also beused as low permittivity insulating layers. Further, in otherembodiments, the diffusion barrier layer may be provided on a surface ofan insulating substrate containing silicate glass or quartz glass forforming gate electrodes with Schottky contact, or source and drainelectrodes with ohmic contact in TFT-LCD devices.

In this embodiment, the insulating layer may be configured from a singleinsulating layer, such as SiOC. Alternatively, other embodiments may usemultilayer structure, such as a silicon nitride (SiN) layer stacked overa silicon oxide carbide (SiOC) layer. Insulating layers with multilayerstructure are advantageous in that the diffusion barrier layer, which isan oxide layer, may effectively be formed on the top surface of themultilayer structure containing oxygen. For example, a diffusion barrierlayer may effectively be formed over an insulating layer with multilayerstructure made from a porous silicon oxide carbide (SiOC) layer, as itsfirst layer, having a plurality of pores with an average pore diameterof about a few nanometers, e.g. 2 nm, and a top layer (second layer),such as a dense SiOC, disposed over the porous SiOC layer.

The diffusion barrier layer pertaining to the preferred embodiments ofthe present invention is a layer where its surface portion is mainlycomposed of copper. The diffusion barrier layer of the preferredembodiments may be formed from a copper alloy layer containing a metalelement, where the metal element can be oxidized easily compared tocopper. Incidentally, an oxide forming enthalpy of copper is −167.5kJ/mol at a temperature of 293K. (see Smithells Metals Reference Book,Seventh Edition, 8-25, Butterworth-Heinemann (1992)). The metal elementwhich is oxidized more easily than copper is a metal element with anenthalpy of oxide formation lower than the enthalpy of oxide formationfor copper at the temperature of 293K. Further, in this embodiment, thecopper alloy layer is a layer composed of a solid solution alloy typecopper, such as a substitutional type, in major proportions. Moreover,the copper alloy layer pertaining to the preferred embodiments of thepresent invention may include a copper layer, a copper-alloy layerincluding copper in major proportions, and a multilayer structureincluding the copper layer or the copper alloy layer and a layer made ofthe metal element where the metal element is oxidized more easilycompared to copper.

In Particular, the copper alloy layer used favorably as a material forforming the diffusion barrier layer of the present invention is a layerincluding a metal element as an additive element which can be easilyoxidized compared to copper. Among various metal elements, those with aneffect of decreasing the type of surface crystal orientation (crystalfaces constituting the surface of the copper alloy layer) after applyinga heat treatment to the copper alloy layer are the most favorable.Without using the copper alloy layer including the metal element, it maybe possible to determine whether the metal element is able to exert suchan action of reducing the type of surface crystal orientation if used inthe copper alloy layer as an additive element. This may be performed byforming a layered structure, in which a layer made of the metal elementis first disposed on the insulating layer. Then, a copper layer isdeposited over the first layer and the type of surface crystalorientation of copper (at deposition) is observed. By applying a heattreatment to the layered structure and examining the surface crystalorientation of copper after the heat treatment it would be possible todetermine whether the type of surface crystal orientation of copper isreduced after the heat treatment.

Different methods may be used to determine the type of surface crystalorientation of copper. Examples of these methods may include an X-raydiffraction (XRD) method, a transmission electron diffraction (TED)method, or a reflection high energy electron diffraction (RHEED) method.The surface crystal orientation referred in the present disclosureexhibits an x-ray diffraction pattern having peaks at diffraction angles(2θ) ranging from 20° to 140°. In the diffraction methods describedabove, e.g. the XRD method, there may be some cases where the x-raydiffraction pattern does not exhibit peaks even though the crystal facesconstituting the actual surface. This is mainly due to the arrangementof atoms within the crystal and their structural factor (“CrystalElectron Microscopy”, by Hiroyasu Saka, Nov. 15, 1997, Uchida RoukakuhoPublishing Co. Ltd., First print, Page 75-81). In the presentdisclosure, the crystal faces generating the diffraction peaks, are atleast “contained” in the surface crystal orientation differing from thecase where the crystal faces are not limited to those generating thediffraction peaks.

As an example, a multilayer structure including a magnesium (Mg) layerwith a thickness of about 20 nm and a copper (Cu) layer with a thicknessof about 150 nm will be explained. The Mg layer and the Cu layer areformed by a high-frequency sputtering method using magnesium of purity(99.9% (=3N)), formed on a SiO₂ layer as an insulating body on a{001}-Si substrate, and using high purity copper of 6N as a target. FIG.1 illustrates an X-ray diffraction pattern taken from the surface of thecopper layer of the multilayer structure after deposition. As shown inthis figure, the XRD pattern illustrates diffraction peaks at thediffraction angles representing the copper crystal faces of {311},{111}, and {200}. Namely, it is shown that the surface of the copperlayer is configured from at least three kinds of crystal faces: {311},{111}, and {001}. Meanwhile, FIG. 2 shows an XRD pattern after heattreating the deposited multilayer structure for 30 minutes at 347° C.(620K). As shown in this figure, the XRD pattern illustrates diffractionpeaks at the diffraction angles representing the copper crystal faces of{111} and {200}. That is, the kinds of surface crystal orientation ofcopper layer is decreased to two: {111} and {001}, after heat treatingthe multilayer structure. Accordingly, it is determined that magnesium(Mg) is a metal element that reduces the types of crystal faceorientation of copper after the heat treatment.

In addition to magnesium (Mg) described above, other metal elements suchas manganese (Mn), aluminum (Al) and the like may also perform theaction of reducing the kinds of surface crystal orientation of copperfrom three kinds at deposition to two kinds by the heat treatment.Similar to the case of magnesium (Mg), the surface crystal orientationof copper may decrease from three kinds at deposition, {311}, {111} and{001}, to two kinds, {111} and {001}, after heat treating the multilayerstructure when the multilayer structure includes a manganese (Mn) oraluminum (Al) layer with a thickness of about 20 nm and a copper layerwith a thickness of about 150 nm formed on the SiO₂ layer, as theinsulating body, on the {001}-Si substrate.

In what follows another example will be described in which a multilayerstructure including a germanium layer (with thickness of about 20 nm)and a copper layer (thickness of about 150 nm) are formed by thehigh-frequency sputtering method using high purity germanium, formed onthe SiO₂ film as an insulating body on the {001}-Si substrate, and usinghigh purity copper of 6N as a target. FIG. 3 illustrates an XRD patterntaken from the surface of the copper layer of the multilayer structureafter deposition. As shown in this figure, the XRD pattern illustratesdiffraction peaks at the diffraction angles representing the coppercrystal faces of {111} and {001}. Namely, it is shown that the surfaceof the copper layer is configured from two kinds of crystal faces: {111}and {001}. Meanwhile, FIG. 4 shows an XRD pattern after heat treatingthe deposited multilayer structure for 30 minutes at 337° C. (610K). Asshown in this figure, the surface crystal orientation of copper layer isreduced down only to {111} crystal face. Based on the results, it isdetermined that germanium (Ge) is a metal element that reduces the kindsof crystal face orientation of the copper layer after the heattreatment.

Favorable heating conditions for decreasing the kinds of copper crystalface orientation is ranging from 327° C. (600K) to 427° C. (700K) intemperature and from one minute to 80 minutes in time. At lowertemperatures, particularly lower than 327° C. (600K), for example at 77°C. (350K), the action of decreasing the type of surface crystalorientation of copper alloy layer may not be clearly determined.Meanwhile, higher temperatures, specifically those exceeding 427° C.(700K), are not preferable because the high temperature causes coppercontained in the copper alloy layer to diffuse and intrude significantlyinto the insulating body, thereby the insulating body decreases itselectrical insulating property. On the other hand, the high temperaturecauses the elements contained in the insulating body, such as silicon,to diffuse and intrude significantly into the copper or copper alloylayer, thereby stable decrease of the kinds of surface crystalorientation is inhibited.

In sum, the favorable heating condition, to obtain a copper layer inwhich the kinds of surface crystal orientation is decreased compared tothe time of deposition, may be performed at temperatures not less than327° C. (600K) and not more than 327° C. (700K), in an inert gasatmosphere, and for a heating time of not less than one minute and notmore than 80 minutes.

Referring back to FIG. 2, the heating condition described above isfavorable for two purposes: 1) decreasing the surface crystalorientation of copper to {111} and {001} crystal faces and 2) obtaininga layer mainly composed of copper where the intensity of X-raydiffraction (XRD) peaks is stronger for the {111} crystal face than forthe {002} crystal face. In this disclosure, “high” or “low” intensityrefers to the number of X-ray counts per second on the X-ray diffractionpattern. It should be noted that although the kinds of surface crystalface orientation is reduced to two, if the surface of the layer mainlycomposed of copper is formed primarily from either type, it maycontribute to the formation of a copper interconnection body with lowdensity of crystal grain boundaries.

The material that favorably provides the diffusion barrier layerpertaining to the present invention is a copper alloy layer containingany one or not less than two metal elements such as magnesium (Mg)(ΔH²⁹³=−601.6 KJ/mol), manganese (Mn) (Δ²⁹³=−1387.5 KJ/mol), germanium(Ge) (Δ²⁹³=−580.2 KJ/mol) or aluminum (Al) (Δ²⁹³=−240.7 KJ/mol). Thesemetal elements are among those that are easily oxidized compared tocopper. The copper alloy layer may include a layer composed of a solidsolution such as a substitutional type. By way of example, the copperalloy layer may include Cu—Mg, Cu—Mn, Cu—Ge, or Cu—Al. Further, thecopper alloy may include a multilayer structure with a copper layer anda magnesium layer or a copper layer and manganese layer.

In particular, the copper alloy layer containing manganese (with adiffusion coefficient of about 1.97×10⁻²⁰ cm²/s at 400° C.) or germanium(with a diffusion coefficient of about 1.13×10⁻¹⁹ cm²/s at 400° C.) mayfavorably be used to form a diffusion barrier layer in which the surfacelayer section is a layer mainly composed of copper. It should be notedthat both manganese and germanium have a diffusion coefficient largerthan the self diffusion coefficient of copper (5.51×10⁻²¹ cm²/s at 400°C.) [Landolt-Bornstein, New Series Group III, Vol. 26, p. 136, SpringerVerlag, Berlin (1990)]. By using the copper alloy layer includingmanganese or germanium as alloying materials, for example, an oxidelayer which constitutes a diffusion barrier layer may be formed in aself forming manner on the insulating layer containing oxygen, as wellas the layer mainly composed of copper may be formed in a self formingmanner on the surface portion of the diffusion barrier layer. This ismainly due to the fact that these metal elements are more easilyoxidized compared to copper and also have diffusion coefficients greaterthan the self diffusion coefficient of copper.

For example, in the case where the diffusion barrier layer is firstformed by depositing a copper layer containing manganese as an additiveelement over an insulating layer made of silicon oxide and then by heattreating the copper layer, the diffusion barrier layer will be made froman oxide layer including manganese, copper and the composing elements ofthe insulating body. For example, the oxide layer may be shown by thefollowing composition formula: Mn_(X)Si_(Y)Cu_(Z)O (O<X, Y, Z<1,X+Y+Z=1, generally, X>Y, Z). Further, the diffusion barrier layer whichis an oxide layer with the above composition formula may be formed byheat treating a multilayer structure as the material for forming thebarrier layer. The multilayer structure may include a copper layerdeposited over a manganese layer, formed on an insulating body made ofsilicon oxide. In addition, the diffusion barrier layer which is anoxide layer with the above composition formula can also be formed bychanging the order of deposition in the multilayer structure.

The copper alloy layer used for forming the diffusion barrier layerpertaining to the present invention may be formed by a high-frequencysputtering method using an alloy material of copper and manganese(Cu—Mn) as target, which contains manganese in a concentration range ofnot less than 5 atom % and not more than 10 atom %. Alternatively, thecopper alloy layer may be formed using copper manganese alloy,high-purity manganese, or high purity copper by a chemical vapordeposition (CVD) method, a high-frequency sputtering method, an ionplating method, a laser ablation method, an electrolytic plating methodand the like. Furthermore, other embodiments may use germanium (Ge) asan alloying material for forming the copper alloy layer using the abovementioned deposition procedures, such as a high-frequency sputteringmethod, a CVD method, an ion plating method, a laser ablation method,and the like. For example, the copper germanium (Cu—Ge) alloy, used inthe above exemplary embodiments, contains germanium in a concentrationrange of not less than 1.0 atom % and not more than 7.0 atom %, forexample, in atomic concentration, high-purity germanium, or high puritycopper.

In a damascene type interconnection structure, the narrower theinterconnection width, provided on an interconnection groove, such astrench groove or via hole of the insulating layer, the thinner is thethickness of the copper alloy layer, which is used as a material forforming the diffusion barrier layer. For example, in a case where theinterconnection width is about 90 nm, the suitable thickness of thediffusion barrier layer for this interconnection width is about 10+/−2nm. Further, in a case where the interconnection width is about 65 nm,the suitable thickness of the diffusion barrier layer is about 7 nm.Furthermore, in a case where the interconnection width is about 32 nm,the suitable thickness of the diffusion barrier layer is about 3.5 nm.Moreover, in a case where the interconnection width is about 22 nm, thethickness of the diffusion barrier layer which is suitable for thisinterconnection width is about 2.5 nm. It is preferable that thethickness of the diffusion barrier layer is set to be not less than 0.5nm regardless of the interconnection width. It is more preferable thatthe thickness of the diffusion barrier layer is set to be not less than1 nm.

When the diffusion barrier layer is made of an ultrathin layer with athickness of about 0.5 to 1 nm, oxygen (O) and silicon (Si), which arethe composing elements of the insulting layer, pass through thediffusion barrier layer and intrude into the copper interconnection bodyprovided on the barrier layer. This results in an inconvenience in thatthe copper interconnection body featuring a low electric resistivity andhigh conductivity can not be obtained. Such an inconvenience may beovercome by providing the diffusion barrier layer pertaining to thepresent invention, in which its surface layer is the layer mainlycomposed of copper, on a layer containing a metal element which isoxidized more easily than silicon (Si).

The enthalpy of oxide formation for silicon is about −910.9 kJ/mol at293K (ΔH²⁹³). In comparison, a metal element which is oxidized moreeasily than silicon is a metal element with the enthalpy of oxideformation lower than silicon. Example of those metal elements mayinclude aluminum (Al), (ΔH²⁹³=−1678.2 KJ/mol), scandium (Sc)(ΔH²⁹³=−1906.7 KJ/mol), titanium (Ti) (ΔH²⁹³=−2457.2 KJ/mol), vanadium(V) (ΔH²⁹³=−1551.3 KJ/mol), chromium (Cr) (ΔH²⁹³=−1130.4 KJ/mol),manganese (Mn) (ΔH²⁹³=−1387.5 KJ/mol), iron (Fe) (ΔH²⁹³=−1117.5 KJ/mol),yttrium (Y) (ΔH²⁹³=−1906.7 KJ/mol), zirconium (Zr) (ΔH²⁹³=−1101.3KJ/mol), niobium (Nb) (ΔH²⁹³=−1900.8 KJ/mol), antimony (Sb)(ΔH²⁹³=−1008.0 KJ/mol), hafnium (Hf) (ΔH²⁹³=−1113.7 KJ/mol), tantalum(Ta) (ΔH²⁹³=−2047.3 KJ/mol), or rhenium (Re) (ΔH²⁹³=−1249.1 KJ/mol). Allof the (ΔH²⁹³) values, described in this paragraph, are cited fromSmithells Metals Reference Book, Seventh Edition, 8-25,Butterworth-Heinemann (1992).

In the case where a layer containing any one or more than one metalelements with the enthalpy of oxide formation lower than silicon, ispositioned between the insulating layer and the diffusion barrier layer,oxygen atoms, which are the composing element of the insulating layerare captured by the metal element. Therefore, the effect of obtainingthe copper interconnection body with low electric resistivity is exertedas the intrusion of oxygen into the copper interconnection body isprevented. In this embodiment, it is preferable that the percentage ofthe total thickness of both layers is set to be not more than about 12%of the interconnection width. For example, the total thickness of thediffusion barrier layer and the layer containing any one or more thanone metal element with the enthalpy of oxide formation lower thansilicon is about 5 nm for an interconnection width of about 45 nm.

It should be noted that, the layer containing the metal element with asignificantly lower enthalpy of oxide formation compared to silicon, butnot more than −1500 kJ/mol of ΔH²⁹³, may easily be oxidized. These metalelements, such as aluminum (Al), scandium (Sc), or vanadium (V), maystructure a layer that can surely prevent the amount of oxygen intrudinginto the copper interconnection body by passing through the diffusionbarrier layer of the present invention. This is mainly due to the easeof oxidation of these metal elements that shows the ease of bonding withoxygen (O) atoms. Further, in other embodiments, the layer may includetantalum (Ta) or titanium (Ti) with the enthalpy of oxide formation notmore than −2000 kJ/mol of Δ²⁹³. By using these metal elements, a layercapable of surely preventing the oxygen (O) from intruding into thecopper interconnection body through the diffusion barrier layer of thepresent invention is formed. This is mainly due to the fact that thesemetal elements are significantly easy to be oxidized. The layercontaining tantalum (Ta) or titanium (Ti) may be formed from a singlelayer titanium or tantalum or formed from tantalum nitride (TaN),titanium nitride (TiN) or the like.

The layer containing any one or more than two metal elements with theenthalpy of oxide formation lower than silicon is formed prior toforming the copper alloy layer on the insulating layer. For example, atantalum or titanium layer may be formed by a high-frequency sputteringmethod using a high purity tantalum or titanium as the target material.Other embodiments may use a chemical vapor deposition (CVD) method usingan organic tantalum compound and the like as a material. Further, in analternative embodiment, a tantalum nitride or titanium nitride layer mayalso be formed by a high-frequency sputtering method, such as a reactiveion sputtering method. In yet another embodiment, the titanium nitridelayer may also be formed by a chemical vapor deposition (CVD) methodusing a titanium compound, such as titanium tetrachloride (TiCl₄) as amaterial.

The diffusion barrier layer is formed by heating the copper alloy layerprovided directly on the insulating layer or on the layer containing anyone or more than two metal elements with the enthalpy of oxide formationlower than silicon. This heat treatment is conducted to diffuse and movethe metal element, which is easily oxidized compared to copper,contained in the copper alloy layer or constitutes the alloy layer in amultilayer structure, into the insulating layer side. This heattreatment is also conducted to form an oxide diffusion barrier layer,which is bond to the oxygen constituting the insulating layer, on theregion that has an interface with the insulating layer. This heattreatment also conducted to provide the diffusion barrier layer in whichits surface layer is mainly composed of copper with high electricalconductivity. In addition, this heat treatment rejects the metal elementfrom copper and accumulates the metal element into the interface regionwith the insulating layer. Therefore, in the preferred embodiment, thecopper alloy layer contains a metal element having the enthalpy of oxideformation lower than copper such that the barrier layer, which is madeof an oxide layer, can be formed on the interface region with theinsulating layer while a layer mainly composed of copper can be formedon the surface portion of the barrier layer.

Favorable temperatures for heating the copper alloy layer are rangingfrom 170° C. to 427° C. (450K-700K). In the case of low temperatures,below 170° C. (450K), the metal element contained in the copper alloylayer, which is oxidized easily compared to copper, can not be diffusedand moved sufficiently into the insulating layer, e.g. SiOC. Therefore,it is inconvenient in that the oxide layer with a sufficient thicknesscan not be stably formed to act as a barrier layer in the interfaceregion with the insulating body. Meanwhile, in the case where the heattreatment is performed at high temperatures, exceeding 427° C. (700K),the thermal diffusion of metal element, e.g. germanium (Ge), to thesurface layer side of the copper alloy layer occurs significantly. Thisresults in forming the layer with a low electric conductivity whichcontains a large amount of germanium accumulating on the surface of thediffusion barrier layer. Consequently, this causes a problem in whichthe copper interconnection body is formed with a low electricresistivity.

The heat treatment of the copper alloy layer is preferably performed inan inert gas atmosphere. Examples of the inert gas atmospheres mayinclude helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) andthe like. Among these inert gas atmospheres, it is preferable to use He,Ne, or Ar for conducting the heat treatment. In addition, it is morepreferable from a view point of economic efficiency to use Ar gas or Hegas atmosphere for the heat treatment.

Furthermore, it is preferable to circulate the inert gas atmosphere,e.g. Ar or He, during the heat treatment of the copper alloy layer. Thisis mainly to sweep the volatile carbon hydride oxide generated from theinsulating layer and also to exhaust the same product from the inert gasatmosphere of the heat treatment, thereby preventing the contaminationof the diffusion barrier layer, for example. It is also preferable toincrease the circulation amount of the inert gas atmosphere as the heattemperature is set to be higher within the preferable temperature rangeas described above. In the case where the heat treatment is performed atthe temperature not less than 600K (327° C.) and not more than 700K(427° C.), the circulation volume of Ar gas is preferably set to about0.1 to 5.0 litters per minute.

It should be noted that the same heat treatment procedure may be appliedfor reducing the kinds of surface crystal orientation of copper,positioned over the diffusion barrier layer, and for forming thediffusion barrier layer itself. For example, by applying the heattreatment at temperatures ranging from 600K to 700K (327° C.-427° C.),the diffusion barrier layer can be formed as well as the layer mainlycomposed of copper in which the kinds of surface crystal orientation isreduced compared to the time when the copper alloy layer is depositedbefore the heat treatment. In this common heat treatment procedure, itis preferable to keep the heating time to 80 minutes. This is mainly dueto the fact that an excess diffusion of metal elements, such asmanganese, occurs if the heating time exceeds 80 minutes fortemperatures ranging from 600K to 700K (327° C.-427° C.). Thereby, thediffusion barrier layer featuring favorable barrier properties can notbe stably formed.

After the heat treatment, copper which will form the interconnectionbody is deposited over the diffusion barrier layer using the layermainly composed of copper as a copper seed layer. The copperinterconnection body may be deposited using a chemical or a physicaldeposition method, such as an electro plating method, an ion platingmethod, or a CVD method. In order to form an interconnection body withlow electric resistivity, the copper deposited over the diffusionbarrier layer is preferably high purity copper containing less metalelement with higher electrical resistivity compared to copper. As forthe metal element with higher electrical resistivity compared to copper,it is possible to use copper with high degree of purity about 99.995%,in which the total contents of aluminum (Al) is not more than 50 weightparts per million (wt·ppm).

EMBODIMENT Embodiment 1

In the following paragraphs, the contents of the first embodimentpertaining to the present invention will be fully explained withreference to FIGS. 5-10. By way of example, the copper interconnectionstructure of the present invention is provided with a diffusion barrierlayer which is in turn formed from a copper alloy layer having amultilayer structure. The multilayer structure is made from the stackedlayers of copper (Cu) and manganese (Mn).

With reference to FIG. 5, a schematic diagram of the first step of aprocess for manufacturing an embodiment of a copper interconnection withsingle damascene structure is shown.

As shown in this figure, a trench form interconnection groove (grooveform opening) 11 is first formed in an insulating layer 10, e.g. SiO₂,with a thickness of 150 nm on a {001}-silicon (Si) substrate, which isnot shown in this figure. The vertical width (opening width) of theinterconnection grove 11 is set to about 32 nm. Then, a manganese layer12 a is deposited over an inner surface and an upper surface side of theinterconnection groove 11 using high purity manganese (degree ofpurity=5N) as a target material by a common high-frequency sputteringmethod. The thickness of the manganese layer 12 a is about 2 nm. Next, acopper layer 12 b with a thickness of about 2 nm is stacked over themanganese layer 12 a by the common high-frequency sputtering methodusing a high purity copper (degree of purity=6N) as a target material.In this way, the copper alloy layer 12 with a multilayer structure isformed. The multilayer structure is formed by the stacking layers ofmanganese 12 a and copper 12 b which are forming materials for thediffusion barrier layer. The environmental pressure for forming themanganese layer 12 a and the copper layer 12 b by the sputtering methodis set to be about 0.6 Pascal (Pa).

Next, the multilayer structure 12 is heated at 357° C. (630K) for 15minutes in argon (Ar) gas flow, thereby forming the diffusion barrierlayer 13. The flow rate of argon gas is set to be about 2.5litter/minute. Referring next to FIG. 6, a schematic diagram of thesecond step of a process for manufacturing an embodiment of a copperinterconnection with single damascene structure is shown. Across-sectional view of the interconnection structure with the diffusionbarrier layer 13 formed in a unit layer after heat treating themanganese layer 12 a and the copper layer 12 b is shown. A commonSecondary Ion Mass Spectroscopy (SIMS) analysis shows that manganese isaccumulated in a concentrated manner on the bottom portion of thediffusion barrier layer 13 at the interface with SiO₂ insulating layer10. Further, the analysis also showed that the atomic concentration ofcopper is increased towards the surface portion of the diffusion barrierlayer 13. Meanwhile, the atomic concentration of manganese is decreasedtowards the surface portion of the diffusion barrier layer 13 whichcorresponds to the increase of the atomic concentration of copper. Thus,the SIMS analysis shows that the surface layer portion of the diffusionbarrier layer 13 is mainly composed of copper.

Further, an Electron Energy Loss Spectroscopy (EELS) method, which isdifferent from the SIMS method, is used for analyzing the distributionof atomic concentration inside of the diffusion barrier layer 13. Inthis analysis, a field emission type transmission electron microscopewith a high resolution is used and the element analysis is performed byscanning an electron beam at 0.2 nm interval. As a result, it is againconfirmed that manganese is accumulated on the bottom portion of thediffusion barrier layer 13 at the interface with insulating layer.Additionally, it is also found that manganese is present mainly as amanganese oxide in the diffusion barrier layer 13. Further, the EELSanalysis shows that a large amount of copper is present on the surfaceportion of the diffusion barrier layer 13. Thus, the EELS analysis alsoconfirms that the surface portion of the diffusion barrier layer 13 ismainly composed of copper.

The surface crystal orientation of the copper alloy layer with themultilayer structure 12, as described above, is examined before andafter the heat treatment process. For this examination, experimentalsamples are prepared separately in order to obtain clear X-raydiffraction patterns from their surface. These experimental samples havesimilar structures as those described above with regard to the firstembodiment, and they feature multilayer structure where a manganeselayer with a thickness of 20 nm and a copper layer with a thickness of50 nm are stacked on a SiO₂ insulating layer, which is provided inseries on a {001}-Si substrate. The same high-frequency sputteringmethod is used for forming the experimental sample with the same formingcondition.

FIG. 7 illustrates an X-ray diffraction (XRD) pattern taken from thesurface of the copper alloy layer 12 with a multilayer structure afterdeposition. As shown in this figure, the XRD pattern illustratesdiffraction peaks at the diffraction angles representing the coppercrystal faces of {311}, {002}, and {111}. That is, the copper surface ofthe experimental sample is configured from three kinds of crystal faces:{311}, {001} and {111}. Meanwhile, FIG. 8 shows an XRD pattern afterheat treating the experimental sample under the same conditions. Asshown in this figure, the XRD pattern illustrates diffraction peaks atthe diffraction angles representing the copper crystal faces of {001}and {111}. That is, the kinds of surface crystal orientation of copperafter heat treating the multilayer structure 12, under the sameconditions, is decreased to two: {001} and {111}.

Since the surface layer portion of the diffusion barrier layer 13 ismainly composed of copper and its surface crystal orientations isconfigured in the {001} and {111} faces after the heat treatment, aburied copper is next deposited on the diffusion barrier layer 13 usingthe layer mainly composed of copper as a copper seed layer. As shownschematically in FIG. 9, the buried copper representing theinterconnection body 14 is formed using an electrolytic plating methodso as to fill inside of the interconnection groove 11. In the last stepof manufacturing process, copper which is excessively formed on theinterconnection groove 11 and the diffusion barrier layer 13 remained onthe insulating layer 10 (SiO₂) are removed by a chemical and mechanicalpolishing (CMP) methods until they reach a level face identical to theupper surface of the insulating layer 10. In this way, a singledamascene type copper interconnection structure 1A is completed asschematically shown in FIG. 10.

The internal structure of the copper interconnection body 14 is examinedby a cross-sectional TEM method using common high resolutiontransmission electron microscopy (HR-TEM). As a result, the number ofcrystal grain boundaries contained in the copper interconnection body 14is found to be about 5/μm² in area density. The area density is thevalue obtained by dividing the number of crystal grain boundary which iscounted in the area examined by the cross-section TEM method, by thearea of the examined area.

Further, the electric resistivity (ρ) of the copper interconnection body14 is measured by direct current four-probe method at room temperature.The electric resistivity (ρ) is calculated using the following formula:P=(π/ln 2)·t·(V/I)·f1·f2   (1)

where t, I, and V represent respectively a thickness of the copperinterconnection body 14, a current (50 mA) conducted into the copperinterconnection body 14 from two probes facing each other at the time ofmeasurement, and a voltage generated when the current I is conductedbetween the other two probes. In this formula, f1 and f2 represent formfactors pertaining to the copper interconnection body 14 (refer to F. M.Smith, The Bell System Technical Journal, 37(1958), P. 711). Theelectric resistivity of the copper interconnection body 14 is calculatedfor the first embodiment and it turns out to be about 2.1 (μΩ·cm), whichis close to the resistivity of pure bulk copper, 1.7 μΩ·cm (refer toJapanese unexamined patent application publication No. H1-202841).

The first embodiment of the present invention will be explained in termsof different materials and deposition order for the copper alloy layer12 with a multilayer structure in two comparative examples.

Comparative Example 1

a trench form interconnection groove 11 with the same opening width (32nm) is formed on the interlayer insulating layer 10 provided on the{001}-silicon (Si) substrate made of the same material (SiO₂) asdescribed before. Thereafter, instead of the stacked layers of manganese(Mn) and copper (Cu), a tantalum nitride (TaN) layer is first depositedover the interlayer insulating layer 10 and then a tantalum layer isdeposited over the TaN layer. In this embodiment, the thickness of eachtantalum nitride and tantalum layers is set to be about 2 nm.

Next, this TaN/Ta double structure is heat treated under the sameconditions (time period, temperature, and atmosphere) as those derivedin the first embodiment described above. After the heat treatmentprocess, a single damascene type copper interconnection structure iscompleted by burying copper into the interconnection groove 11 using theelectrolytic plating method as described above in the first embodiment.

The internal structure of the copper interconnection body 14 is examinedusing the cross-sectional TEM method. The number of crystal grainboundary contained in the copper interconnection body 14 is about 14/μm²in area density. In this embodiment, the area density of the crystalgrain boundary is higher by about 1 digit compared to the case where thecopper interconnection body 14 is formed over the diffusion barrierlayer 13, which is made from the stacked layers of manganese and copper.Because the interconnection body 14 is formed from the copper containingthe crystal grain boundaries in high density, the electric resistivityof the copper interconnection body 14, identically measured using thedirect current four-probe method, is about 4.5 μΩ·cm at roomtemperature, which is about twice as large as that in the case of firstembodiment.

To understand the resulting effect of higher amount of crystal grainboundaries in the copper interconnection body 14, experimental sampleshaving similar structure as those described in the above structure areexamined. The experimental samples used in our analysis feature amultilayer structure with the stacking layers of tantalum (thickness ofabout 20 nm) and copper (thickness of about 150 nm) on the SiO₂insulating layer provided in series on the {001}-Si substrate.

FIG. 11 illustrates an XRD diffraction pattern taken from the surface ofthe copper layer of the experimental samples at the time of deposition.As shown in this figure, the XRD pattern illustrates diffraction peaksat the diffraction angles representing the copper crystal faces of{311}, {111}, and {001}. Further, FIG. 12 illustrates an XRD patternafter the experimental samples undergoes a heat treatment process underthe same conditions as those described in the first embodiment. As shownin FIG. 12, the XRD pattern illustrates the same copper crystal faces,{311}, {111}, and {001}, even after performing the heat treatment. Thatmeans, in the case of tantalum layer, the action of reducing the kindsof surface crystal orientation, which is provided by bonding to thetantalum layer, is not observed significantly after the heat treatmentprocess. Therefore, it is interpreted as the main reason for resultingin a polycrystalline copper on the tantalum layer, where thepolycrystalline copper features an intricate crystalline structure witha high density of crystal grain boundaries with various crystal faces ofdifferent face orientations.

Comparative Example 2

Similar to the first embodiment, a trench form interconnection groove 11with an opening width of 32 nm is formed on the SiO₂ interlayerinsulating layer 10 provided on a {001}-silicon (Si) substrate. On anupper surface of the interlayer insulating layer 10 and an inner surfaceof the interconnection groove 11, the copper layer and the manganeselayer are deposited by the common high-frequency sputtering method. Inthis embodiment, the order of the stacking layers is changed from thefirst embodiment. The thickness of the copper layer is set to about 2nm, which is the same as in the case of the first embodiment. Meanwhile,the thickness of the manganese layer is set to about 3 nm, which isthicker compared to the case of the first embodiment. This is mainly dueto the fact that in this embodiment the manganese layer is positionedfar from the surface of the insulting layer 10 for providing the copperinterconnect structure.

Next, the multilayer structure, made of the copper layer and themanganese layer which are materials for forming the diffusion barrierlayer 13, is heat treated for 30 minutes at 650K in argon gas flow at aflow rate of about 3.0 litter/minute. In this embodiment, the heattreatment process is performed in a higher temperature range and for alonger period of time compared to the case of the first embodiment. Thisis to surely form the diffusion barrier layer 13, which is mainlycomposed of manganese oxide, in the region in close proximity with theinsulating layer 10 by sufficiently diffusing manganese towards theinterlayer insulating layer 10, which is positioned, in this embodiment,far from the insulation layer through the copper layer.

After forming the diffusion barrier layer 13 by heat treating themultilayer structure, which is configured by reversing the stackingorder compared to the first embodiment, the distribution of atomicconcentration in the thickness direction of the diffusion barrier layer13 is measured by the SIMS method. According to SIMS analysis, it isfound that manganese diffuses and moves to a region in close proximityto the interface with the SiO2 insulating layer 10 and is concentratedin this region. Although there is a difference in the atomicconcentration, the oxygen atoms inside of the diffusion barrier layer 13show a similar state of distribution as manganese atoms. Meanwhile, itis shown that the copper is accumulated on the surface portion of thediffusion barrier layer 13. Further, even though the multilayerstructure is formed by changing the deposition order, the micro X-raydiffraction pattern (XRD) shows that the surface portion of thediffusion barrier layer 13 is configured from copper crystal faces of{001} and {111}. Additionally, the XRD pattern after conducting the heattreatment shows that an intensity of {111} face is about ten timesstronger than that of {002} diffraction peak (refer to FIG. 8).

Similar to the case of the first embodiment, copper constituting theinterconnection body 14 is deposited on the diffusion barrier layer 13by the electrolytic plating method using the layer mainly composed ofcopper as a copper seed layer. This is due to the fact that the surfaceportion of the diffusion barrier layer 13 is mainly composed of copperwith two kinds of surface crystal orientation: {001} and {111} afterconducting the heat treatment. Next, copper which is excessively formedon the interconnection groove 11 and the diffusion barrier layer 13remained on the upper surface of the insulating layer 10 (SiO₂) areremoved by a chemical and mechanical polishing (CMP) method until theyreach a level face identical to the upper surface of the insulatinglayer 10. Thereby, a single damascene type copper interconnectionstructure 1A is completed, as schematically shown in FIG. 10.

The internal structure of the copper interconnection body 14 is examinedby a cross-sectional TEM method using common HR-TEM. The number ofcrystal grain boundary contained in the copper interconnection body 14is about 5/μm² in area density, which is the same as in the case of thefirst embodiment. Further, the electrical resistivity of the copperinterconnection body 14 is measured by the direct current four-probemethod at room temperature. The result of this measurement shows a smallvalue (2.2 μΩ·cm), as in the case of the first embodiment, which isclose to the resistivity of pure bulk copper (1.7 μΩ·cm).

Embodiment 3

The third embodiment of the present invention is explained using anexample, in which the diffusion barrier layer 13 is formed from a coppermanganese (Cu—Mn) alloy layer.

First, a trench form interconnection groove 11 is formed on a SiOClayer, insulating layer 10 provided on the {001}-silicon substrate, witha thickness of 120 nm by common plasma etching method. The opening widthof the interconnection groove 11 is set to 32 nm. Second, acopper-manganese (Cu—Mn) alloy layer is deposited onto an upper surfaceof the SiOC insulating layer 10 and an inner surface of theinterconnection groove 11 by a common high-frequency sputtering methodusing the Cu—Mn alloy as a target, in which the atomic concentration ofmanganese is about 7 atom % in concentration. The thickness of the Cu—Mnalloy layer is set to be about 2 nm. The environmental pressure forforming the copper-manganese (Cu—Mn) alloy layer is set to be 0.1 Pascal(Pa).

Next, the copper-manganese (Cu—Mn) alloy layer is heated for 10 minutesat a temperature of about 610K (337° C.) in argon (Ar) gas flow to formthe diffusion barrier layer 13. The flow rate of argon is set to beabout 2.0 litter/minute. By this heat treatment, manganese atomsdiffuses and accumulates in a concentrated manner in a region in closeproximity to the SiOC insulating layer 10, thereby an amorphous layermade of manganese oxide containing carbon is formed with sufficientbarrier properties. Meanwhile, the surface portion of the diffusionbarrier layer 13 is formed as a layer mainly composed of copper, whichcontains more copper than manganese.

The surface crystal orientation of the copper-manganese (Cu—Mn) alloylayer before and after the heat treatment is analyzed using the XRDdiffraction method. Before applying the heat treatment, the XRD patternillustrates three kinds of copper crystal faces: {311}, {001} and {111}.Meanwhile, the XRD pattern shows that the kinds of copper surfaceorientations are reduced to two types: {001} and {111}, after applyingthe heat treatment. Additionally, according to the XRD analysis, theintensity of {111} diffraction peak is about ten times stronger thanthat of {002} diffraction peak.

Because the surface layer portion of the diffusion barrier layer 13 ismainly composed of copper and the surface crystal orientation isconfigured from {001} and {111} copper crystal faces, a buried copper,which constitutes the interconnection body 14, is deposited on thediffusion barrier layer 13 by the electrolytic plating method using thelayer mainly composed of copper as a copper seed layer. After depositingthe buried copper inside of the interconnection groove 11, the diffusionbarrier layer 13 remained on the SiOC insulating layer 10 and copperexcessively formed on the interconnection groove 11 are removed by thechemical and mechanical polishing (CMP) method until they reach thelevel face identical to the upper surface of the SiOC insulating layer10. In this way, a single damascene type copper interconnectionstructure 1A is completed as shown schematically in FIG. 10.

The internal structure of the copper interconnection body 14 is examinedby a cross-sectional TEM method using common HR-TEM. The number ofcrystal grain contained in the copper interconnection body 14 is 6/μm²in area density. Furthermore, the electric resistivity of the copperinterconnection body 14 is measured at room temperature by the directcurrent four-probe method. The result of this measurement shows lowvalue about 2.0 μΩ·cm, which is close to the electric resistivity ofpure bulk copper (1.7 μΩ·cm).

Embodiment 4

The fourth embodiment of the present invention is explained withreference to FIG. 13 using an example in which the copperinterconnection structure is provided with a double diffusion barrierlayer formed from tantalum series and copper-manganese (Cu—Mn) alloymaterials.

With reference to FIG. 13, a cross-sectional view of an alternativeembodiment of copper interconnection structure is shown. In thisembodiment, the diffusion barrier layer is formed from a multilayerstructure 22 including the tantalum series layer 22 a and 22 b and thecopper-manganese (Cu—Mn) alloy layer 22 c in a damascene type copperinterconnection structure 1B.

As schematically shown in FIG. 13, a trench form interconnection groove21 with an opening width of 45 nm is formed on an insulating layer 20,SiON, with a thickness of about 150 nm on a {001}-silicon (Si)substrate, not shown in this figure, by a common plasma etching method.First, a tantalum nitride layer 22 a is deposited onto the upper surfaceof the SiON insulating layer 20 and the inner surface of theinterconnection groove 21 by a common reactive ion sputtering methodusing high purity tantalum as a target material and nitride (N₂) gas asa nitride source. The thickness of the tantalum nitride layer 22 a isset to be about 2 nm. Next, a tantalum layer 22 b with the thickness ofabout 2 nm is stacked on the tantalum nitride layer 22 a by a commonhigh-frequency sputtering method using high-purity tantalum as a targetmaterial.

Then, a copper-manganese (Cu—Mn) alloy layer 22 c is deposited over thetantalum layer 22 b forming a multilayer structure 22 used as materialsfor forming the diffusion barrier layer 23. The copper alloy layer 22 ccontains manganese (Mn) in a concentration range of 10 atom % and itsthickness is set to be about 5 nm. The environmental pressure forforming the copper-manganese alloy layer 22 c, by a commonhigh-frequency sputtering method, is set to be about 0.07 Pascal (Pa).

Next, the multilayer structure 22 is heated for 7 minutes at atemperature of about 660K (387° ) in Argon (Ar) gas flow, thereby thediffusion barrier layer 23 is formed. The flow rate of argon gas is setto be about 4.0 litter/minute. Using the common SIMS analysis, it isshown that manganese is diffused and accumulated in a concentratedmanner toward the tantalum layer 22 b inside the copper-manganese(Cu—Mn) alloy layer 22 c. The concentration of oxygen atoms inside thecopper-manganese (Cu—Mn) alloy layer 22 c is about 4×10¹⁸ cm⁻³, which islower compared to the case where the copper-manganese (Cu—Mn) alloylayer 12 is directly deposited on the insulating layer 10, SiON, andheat treated as in the case of the third embodiment described above. Inthe region where the manganese atoms are accumulated, oxygen atomsshowing similar concentration distribution are also accumulated.Therefore, an amorphous manganese oxide with a thickness of about 3nm isformed in close proximity to the region where the manganese and oxygenatoms are accumulated.

Furthermore, it is shown that on the surface layer portion of thecopper-manganese (Cu—Mn) alloy layer 23 c, the atomic concentration ofcopper is increased which corresponds to the gradual decrease of theatomic concentration of the manganese towards the surface. It is alsoshown that the region of depth about 2 nm from the surface of thecopper-manganese alloy layer 23 c towards the tantalum layer 23 b hasbecome a layer mainly composed of copper. The surface crystalorientation of the multilayer structure 22 (diffusion barrier layer 23)is analyzed before and after the heat treatment using the XRDdiffraction method. The results of XRD method confirm that the surfaceof the copper-manganese (Cu—Mn) alloy layer 22 c, which constitutes theupper most layer of the multilayer structure 22 before the heattreatment, is configured from three kinds of copper crystal faces:{311}, {001}, and {111}. Meanwhile, the surface of the diffusion barrierlayer 23 obtained by heat treating the multilayer structure 22 isconfigured from two kinds of copper crystal faces: {001} and {111}.Furthermore, the XRD analysis confirms that the intensity of {001}diffraction peak is about ten times higher than that of the {002}crystal face after applying the heat treatment.

Because the surface layer portion of the diffusion barrier layer 23 ismainly composed of copper and the surface crystal orientation isconfigured from {001} and {111} copper crystal faces after the heattreatment, a buried copper which constitutes the interconnection body 24is deposited on the diffusion barrier layer 23 by electrolytic platingmethod using the layer mainly composed of copper as a copper seed layer.After depositing the buried copper inside of the interconnection groove21, the multilayer structure 22 remained on the SiON insulating layer 20and the copper excessively formed on the interconnection groove 21 areremoved by the chemical and mechanical polishing (CMP) method until theyreach the level face identical to the upper surface of the insulatinglayer 20. Thereby, a single damascene type copper interconnectionstructure 1B is completed as shown schematically in FIG. 13.

Internal structure of the copper interconnection body 24 is examined bythe cross-sectional TEM method using common HR-TEM. The number ofcrystal grain boundary contained in the copper interconnection body 24is 3/μm² in area density. Further, electric resistivity of the copperinterconnection body 24 is measured at room temperature by the directcurrent four-probe method. The result of this measurement shows a lowvalue about 2.1 μΩ·cm, which is close to the electric resistivity ofpure bulk copper (1.7 μΩ·cm).

Embodiment 5

The fifth embodiment of the present invention is explained using anexample, in which the copper interconnection structure is provided withthe diffusion barrier layer, which is formed from a tantalum serieslayer, a manganese layer, and a copper layer.

In this embodiment, similar to the previous cases, a trench forminterconnection groove 21 with an opening width of 45 nm is formed by acommon plasma etching method on a so-called porous SiOC layer with voidfraction of about 30% having a plurality of fine pores with the averagepore diameter of about 2 nm to 3 nm. Thereafter, the damages resultedfrom the plasma etching are repaired using an organic silane based gas.

Thereafter, the tantalum nitride layer 22 a with a thickness of about 2nm, the tantalum layer 22 b with a thickness of about 2 nm, and amanganese layer with a thickness of about 2 nm are depositedrespectively on the upper surface of the SiOC insulating layer 20 andthe inner surface of the interconnection groove 21 using the samemethods as those described above in the fourth embodiment.

Next, the heat treatment process is performed for 30 minutes at atemperature of 650K (377° C.) in the argon (Ar) atmosphere containing 25parts per million (vol.ppm) of oxygen in volume ratio. The rate oftemperature increase from the room temperature to the heat treatmenttemperature of 650K is 8K per minute. Further, the average cooling speedfrom 650K to room temperature after the heat treatment is 10K perminute. By this heat treatment, the manganese layer is oxidized andconverted into the amorphous manganese oxide layer realizing the barrierproperty.

After heat treating the manganese layer, a copper layer with a thicknessof 3 nm is deposited over the manganese oxide layer to form themultilayer structure 22 using high purity (purity=6N) copper as a targetby the high-frequency sputtering method. The total thickness of thecopper-manganese (Cu—Mn) alloy film 22 c, in this embodiment, is made tobe about 5 nm. The environmental pressure for forming thecopper-manganese alloy layer 22 c, by the common high-frequencysputtering method, is set to be about 0.07 Pascal (Pa). Using the XRDanalysis, it is confirmed that the surface of copper layer at the timeof deposition is configured from three kinds of crystal faces: {311},{001}, and {111}.

Thereafter, the multilayer structure 22 is heat treated for 10 minutesat a temperature of 650K in Argon (Ar) gas flow with the flow rate of3.0 litter/minute. Similar to the previous embodiments, the XRD analysisconfirms that the kinds of surface crystal orientation of copper, theuppermost layer of the multilayer structure 22, is reduced to two types,{111} and {001}, after this heat treatment. In addition, the XRDanalysis illustrate that the intensity of X-ray diffraction peak of{111} face, after the heat treatment process, is about ten times higherthan the intensity of X-ray diffraction peak of {200} face.

Next, a buried copper, which constitutes the interconnection body 24, isdeposited on the barrier layer 23 by the common electrolytic platingmethod using the copper layer having the {001} and {111} crystal faceson its surface as a copper seed layer. The buried copper is provided soas to bury inside of the interconnection groove 21. After depositing theburied copper inside of the interconnection groove 21, the multilayerstructure 22 remained on the SiOC insulating layer 20 and the copperexcessively formed on the interconnection groove 21 are removed by theCMP method until they reach the level face identical to the uppersurface of the insulting layer 20. In this way, a single damascene typecopper interconnection structure 1B is completed as shown schematicallyin FIG. 13.

The internal structure of the copper interconnection body 24 is examinedby a cross-sectional TEM method using common HR-TEM. The number ofcrystal grain boundary contained in the copper interconnection body 24is 7/μm² in area density. Further, the electric resistivity of thecopper interconnection body 24 is measured at room temperature by thedirect current four-probe method. The result of this measurement shows alow value about 2.3 μΩ·cm, which is close to the electric resistivity ofpure bulk copper (1.7 μΩ·cm).

Embodiment 6

The sixth embodiment of the present invention is explained using anexample, in which the copper interconnection structure is provided witha diffusion barrier layer using a germanium (Ge) layer and acopper-manganese (Cu—Mn) alloy layer as materials.

Similar to the first embodiment, a trench form interconnection groove 11with an opening width of 32 nm is formed on the SiO₂ insulating layer 10provided on the {001}-silicon (Si) substrate. Onto the upper surface ofthe interlayer insulating layer 10 and the inner surface of theinterconnection groove 11, a germanium (Ge) layer and copper-manganese(Cu—Mn) alloy layer are deposited in series by the common high-frequencysputtering method. The germanium layer is formed using the common highfrequency sputtering method and its thickness is set to 2 nm.

In this embodiment, the copper-manganese (Cu—Mn) alloy layer is formedby the common high-frequency sputtering method using the (Cu—Mn) alloyas a target containing manganese in a concentration range of 7 atom %.The thickness of the copper-manganese (Cu—Mn) alloy layer is set to 5nm, which is thicker compared to the case of the first embodiment. Thisis to further suppress the diffusion and intrusion of germanium into thesurface layer portion of the copper-manganese (Cu—Mn) alloy layerconsidering the fact that germanium has relatively greater diffusioncoefficient (the diffusion coefficient of Ge at 400° C. is 1.13×10⁻¹⁹cm²/s) compared to copper.

In the next step, the multilayer structure made of germanium layer andcopper-manganese (Cu—Mn) alloy layer, which are materials for formingthe diffusion barrier layer, is heat treated for one minute at 605K(332° C.) in argon gas flow at a flow rate of 1.0 litter/minute. Inorder to suppress the diffusion of germanium into the copper-manganese(Cu—Mn) alloy layer, the heat treatment is performed using a commoninfrared lamp annealing method which can reduce the heating time. Thetemperature is then increased from room temperature to 605K in fiveseconds. The lamp is then turned off one minute after the temperaturereaches to its desired level, and the flow rate of the argon gas, whichis circulated in the heat treatment environment, is increased to 8litter/minute in order to promote the cooling of the multilayerstructure 12.

After forming the diffusion barrier layer 13 by heating the multilayerstructure 12, the distribution of atomic concentration in the thicknessdirection of the diffusion barrier layer 13 is measured by the SIMSmethod. According to the SIMS analysis, it is found that manganesediffuses and moves to a region in close proximity to the interface withthe SiO₂ insulating layer 10 and is distributed in a concentrated mannerin this region. Although there is a difference in the atomicconcentration, oxygen atoms inside of the diffusion barrier layer 13show similar state of distribution as manganese atoms. Based on theresult of EELS analysis, it is determined that an amorphous manganeseoxide is formed in the region where the manganese and oxygen atoms areaccumulated. Further, germanium is also present in this region thoughits atomic concentration is less than that of manganese.

Meanwhile, it is shown that copper is accumulated on the surface portionof the diffusion barrier 13, opposite side of the interface between thebarrier layer 13 and the SiO2 insulating layer 10. Further, the surfacecrystal orientation of the multilayer structure 12(13) is examinedbefore and after the heat treatment process by the XRD analysis. Thisanalysis shows that the surface of the copper-manganese (Cu—Mn) alloylayer is configured from copper crystal faces of {001} and {111} beforethe heat treatment. On the contrary, only the {111} diffraction peak ofcopper is appeared in the XRD pattern of the copper-manganese (Cu—Mn)alloy layer after the heat treatment (refer to FIGS. 3 and 4).

After the heat treatment process, a buried copper, constituting theinterconnection body 14, is deposited on the diffusion barrier layer 13,where its surface layer is mainly composed of copper with surfacecrystal orientation of {111} face, by the electrolytic plating methodusing the layer mainly composed of copper as a copper seed layer. Next,the diffusion barrier layer 13 remained on the SiO₂ insulating layer 10and the copper excessively formed on the interconnection groove 11 areremoved by CMP method until they reach a level face identical to theupper surface of the insulating layer 10. Thereby, a single damascenetype copper interconnection structure 1A is completed as schematicallyshown in FIG. 10.

The internal structure of the copper interconnection body 14 is examinedby a cross-sectional TEM method using common HR-TEM. The number ofcrystal grain boundary contained in the copper interconnection body 14is 7/μm² in area density, which is lower compared to the case of thefirst embodiment. Meanwhile, the electric resistivity of the copperinterconnection body 14 v is measured by the direct current four-probemethod at room temperature. The result of this measurement shows a lowvalue, 2.5 μΩ·cm, which is higher than the case of the first embodimentbut is lower than the resistivity of pure aluminum (2.7 μΩ·cm). Thishigher resistivity may be interpreted, based on the SIMS analysis, as anintrusion of small amount of germanium (<1×10¹⁸ atom/cm³) into theinterconnection body 14 such that the interconnection body 14 may not beconfigured from the pure bulk copper.

Embodiments of the copper interconnection structure pertaining to thepresent invention are low in the density of crystal grain boundaries andelectrical resistivity, therefore they are favorable for effectivelycirculating the device operating current. Further, the copperinterconnection structures of the present invention are also superior inEM resistance and are capable of avoiding the leakage of the deviceoperating current. Therefore, they are favorable to be used formanufacturing electronic devices with low electric consumption and highoperating reliability, such as liquid crystal display (LCD) devices,flat display panel (FDP) devices, organic electroluminescence (EL)devices, and inorganic EL devices.

Embodiments of the copper interconnection structure with a low densityof crystal grain boundaries and low electrical resistance, pertaining tothe present invention, may be formed in interconnections with aninterconnection width of 45 nm, or fine interconnections with aninterconnection width of 32 nm or less, with advanced technology nodefor new generation of interconnection structures. Therefore, thesecopper interconnection structures may be used to manufacture siliconUSLI devices with an interconnection width of 45 nm or less, forexample.

Furthermore, the copper interconnection structure pertaining to thepresent invention features a low electric resistance. Thus, these copperinterconnection structures may be favorably used for manufacturingsilicon semiconductor memories, such as a NAND type flash memory with alow RC delay.

What is claimed is:
 1. A method for forming a copper interconnectionstructure, the method comprising the steps of: forming an opening in aninsulating layer; forming a copper alloy layer including a metal elementon an inner surface of the opening, wherein an enthalpy of oxideformation for the metal element is lower than the enthalpy of oxideformation for copper; and conducting a heat treatment on the copperalloy layer so as to form a barrier layer, wherein: said heat treatmentis conducted: at temperatures ranging from 327° C. to 427° C., for atime period ranging from 1 minute to 80 minutes, and the copper alloylayer including the metal element comprises copper surface orientationof {111}, {001}, and {311} and the step of conducting the heat treatmentcomprises a step of removing the copper surface orientation of {311}. 2.The method as recited in claim 1, wherein an atomic concentration of themetal element in the barrier layer is accumulated toward an outersurface of the barrier layer facing the insulating layer, and an atomicconcentration of copper in the barrier layer is accumulated toward aninner surface of the barrier layer.
 3. The method as recited in claim 2,wherein the barrier layer further comprises an atomic concentration ofoxygen accumulated toward the outer surface of the barrier layer showingsimilar distribution as the atomic concentration of the metal element.4. The copper interconnection structure of claim 1, wherein the heattreatment is conducted in an inert gas atmosphere with a flow rate ofnot less than 0.1 liter per minute and not more than 5.0 liter perminute.
 5. The copper interconnection structure of claim 1, wherein themetal element has a diffusion coefficient greater than a self diffusioncoefficient of copper.
 6. The copper interconnection structure of claim1, wherein the metal element comprises at least one or more of magnesium(Mg), manganese (Mn), aluminum (Al) and germanium (Ge).
 7. The method asrecited in claim 1, wherein the copper alloy layer is formed in a vacuumatmosphere with a pressure of not more than 1 Pascal.
 8. The method asrecited in claim 7, wherein the copper alloy layer is formed in a vacuumatmosphere with a pressure of not more than 0.1 Pascal.
 9. The method asrecited in claim 1, wherein the copper alloy layer is formed from coppermanganese alloy.
 10. The method as recited in claim 1, wherein thecopper alloy layer has a multilayer structure.
 11. The method as recitedin claim 10, wherein the multilayer structure comprises a layerincluding copper and a layer including manganese with an interchangeableorder of deposition over the insulating layer.
 12. The method as recitedin claim 10, wherein the multilayer structure comprises: a first layerincluding germanium formed on the insulating layer, and a second layerincluding copper manganese alloy deposited over the first layer.
 13. Themethod as recited in claim 1, further comprising a step of forming alayer comprising a second metal element on the insulating layer beforeforming the copper alloy layer.
 14. The method as recited in claim 13,wherein an enthalpy of oxide formation for the second metal element islower than the enthalpy of oxide formation for silicon.
 15. The methodas recited in claim 13, wherein the second metal element comprises atleast one of scandium (Sc), titanium (Ti), vanadium (V), chrome (Cr),yttrium (Y), zirconium (Zr), niobium (Nb), antimony (Sb), hafnium (Hf),tantalum (Ta) and rhenium (Re).
 16. The method as recited in claim 15,wherein the second metal element comprises tantalum or titanium.
 17. Themethod as recited in claim 13, wherein the layer comprising the secondmetal element has a multilayer structure.
 18. The method as recited inclaim 17, wherein the multilayer structure comprises: a first layercomprising tantalum nitride formed on the insulating layer, and a secondlayer comprising tantalum formed over the first layer.
 19. The method asrecited in claim 1, wherein an intensity of X-ray diffraction peak of{111} face is stronger than an intensity of X-ray diffraction peak of{200} face.
 20. The method as recited in claim 19, wherein the intensityof X-ray diffraction peak of {111} face is about 10 times stronger thanthe intensity of X-ray diffraction peak of {200} face.
 21. The method asrecited in claim 1, further comprising a step of depositing copper overthe inner surface of the barrier layer so as to form an interconnectionbody.